AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Effect of Sodium Chloride on the Evolution of Size and Mixing State of Soot Particles from a Sooting Laminar Diffusion Flame
MOHSEN KAZEMIMANESH, Chen Kuang, Larry W. Kostiuk, Jason S. Olfert, University of Alberta
Abstract Number: 330 Working Group: Combustion
Abstract With global flaring volumes exceeding 140 billion m3 annually, flares are an important source of anthropogenic pollutants, such as black carbon. Hydraulic fracturing, which is a ubiquitous practice in the upstream oil and gas industry, introduces a new concern about the potential pollutants from flares as a result of flowback operations as the final stage of hydraulic fracturing. In this study, we used an open-tip sooting laminar diffusion flame, with and without sodium chloride particles introduced into the fuel flow prior to combustion, to study the effect of the latter on the evolution of size and mixing state of the particulate emissions. Methane was used as a fuel, which is a significant fraction of global flare gas. A Santoro burner was used and a 30 mm i.d. quartz tube with a length of 51 mm was placed around the fuel tube to produce a sooting laminar diffusion flame with a visible height of ~110 mm. The fuel and the overall co-flow air flow rates were 0.261 and 27.5 standard L/min, respectively. The sodium chloride concentration at the fuel outlet was ~45 ng/cm3. A 3.1 mm stainless steel tube with a 0.3 mm orifice was used to extract the sample and dilute it immediately by a factor of 1,000–12,000. The diluted sample was subsequently forwarded to a scanning mobility particle sizer and a transmission electron microscopy (TEM) sampler to study the size distributions and mixing state of particles, respectively.
The results show that in the case of the methane-only flame, the particle mode diameter increased from 56 to 77 nm with increasing HAB from 47 to 72 mm due to coagulation, although it decreased locally to ~60 nm at HAB range of 72-102 mm due to partial oxidation of soot particles near the open tip of the flame and remained constant in diameter up to height of 207 mm. In the height range of 207-437 mm, the particle mode diameter increased to ~100 nm due to further coagulation. The particle concentration in the overall HAB range decreased by two orders of magnitude from 2×1010 cm−3. In the case of methane-NaCl flame, the mode diameter increased from 39 to 45 nm in the HAB range of 47-72 mm; however, the coagulation rate was lower in this range and particles were smaller with greater concentration compared to the methane-only flame. Particles grew from 45 to 92 nm in the height range of 72-237 mm due to gradual coagulation. At HAB=287-487 mm, three modes were observed in the size distribution, with the first two modes at ~8 and 25 nm due to nucleation of NaCl particles from its vapour phase and the third mode at ~100 nm from soot particles. With further increase in HAB up to 537 mm, the size distribution became bimodal with the first mode at 25 nm and the second mode at 140 nm, while the concentration of the latter was relatively lower than that of the former. The soot particles became larger due to coagulation, either with soot or NaCl particles. The TEM images showed that until HAB of ~287 mm, the NaCl could not re-nucleate from its vapour phase due to elevated temperatures; however, at higher HABs, spherical or cubic particles of NaCl were observed mostly externally mixed and rarely internally mixed with soot particles. The size of NaCl particles from TEM images was consistent with the sizes seen in the particle size distributions.